Chemical bonding

Why do atoms combine?

To achieve stable electronic configuration of a noble gas

Group 18 elements have a? This makes them?

Fully-filled valence electron shell → stable, chemically unreactive, monoatomic

How do atoms chemically bond and combine?

Either:

1. Lose valence electrons

2. Gain valence electrons

3. Share valence electrons

What is a chemical bond?

A region that forms when electrons from different atoms interact with each other.

Which electrons participate in chemical bonding?

Valence electrons.

What are the types of chemical bonds focused on this year?

Ionic bonding

Covalent bonding

What is ionic bonding?

A transfer of electron(s) from a metal to a non-metal atom, resulting in an electrostatic force of attraction between the oppositely charged ions in order to gain the electronic configuration of a noble gas.

What are the two types of ions?

Cations

Anions

What are cations

Positively charged ions (loses electrons, fewer electrons than protons)

So, what do metals do?

Lose valence electrons to form cations

What are anions?

Negatively charged ions (gain electrons, more electrons than protons)

What do non-metals do?

Gain valence electrons to form cations.

The names of non-metal ions would end with?

-ide

All ions have?

The electronic configuration of a noble gas

Group 14 elements do not? instead they?

They do not form ions. They tend to share electrons with other elements to form covalent molecules.

Group 18 elements - can they form ions?

No, as they already have a fully-filled valence electron shell (full-shell structure)

How do we determine valency/charge?

Group of elements in the periodic table.

E.g.

grp 1 → +

grp 2 → 2+

grp 13 → 3+

grp 14 shares electrons

grp 15 → 3-

grp 16 → 2-

grp 17 → 1-

(metal loses, non-metal gains)

What keeps ions bonded?

The strong electrostatic forces of attraction, called an ionic bond.

How are ionic compounds formed?

When oppositely charged ions are attracted to form a neutral compound.

What do we call ions that contain more than one atom?

Polyatomic ions

What are the polyatomic ions you must MEMORISE this year?

NH₄⁺ (AMMONIUM ION)

OH⁻ (HYDROXIDE ION)

NO₃⁻ (NITRATE ION)

SO₄²⁻ (SULFATE ION)

CO₃²⁻ (CARBONATE ION)

NO₂⁻ (NITRITE ION)

SO₃²⁻ (SULFITE ION)

HCO₃⁻ (HYDROGENCARBONATE/BICARBONATE ION)

MnO₄⁻ (MANGANATE(VII) ION)

Cr₂O₇²⁻ (DICHROMATE ION)

PO₄³⁻ (PHOSPHATE ION)

What conventions should we follow?

A positive ion is always written first, then the negative ion

Ions are written as a subscript after the chemical symbol. e.g. MgCl₂

If more than one polyatomic ion is required to balance the charges, the number of polyatomic ions is written as a subscript after the bracketed group of atoms.

e.g. Iron(III) sulfate: Fe₂(SO₄)₃. Ratio of Fe³⁺ to SO₄²⁻ is 2:3

Transition metals have?

Variable charges that are indicated by Roman numerals in the compound’s name.

What do ionic compounds exist as a?

A giant ionic lattice structure (crystals)

Due to their structure, they have what physical properties?

Very high melting and boiling points compared to covalent molecules

Ionic salts are readily soluble in water

Only conduct electricity in aqueous or molten (liquid) state

Very hard
Very brittle

Explain Very high melting and boiling points compared to covalent molecules

Ionic compounds have a giant ionic lattice structure. A large amount of energy is required to overcome the strong electrostatic forces of attraction between the oppositely charged ions

Explain Ionic salts are readily soluble in water

Due to the dipole nature of water, water is able to attract the ions in the giant ionic lattice structure and break the structure apart.

Explain Only conduct electricity in aqueous or molten (liquid) state

Due to the presence of mobile/freely-moving ions

(In the solid state, the ions are held tightly in fixed positions in the giant ionic lattice structure, hence the ions are not able to move freely to conduct electricity)

Explain very hard

There are strong electrostatic forces of attraction (ionic bonds) between the oppositely charged ions that hold the structure together

Explain very brittle

When a force is applied, the layers of ions are shifted, and when like charges align, electrostatic repulsion occurs, and the structure is broken.